Spring MVC 源码分析

 

Spring MVC

SpringMVC中扮演关键角色的DispatcherServlet类。

1 DispatcherServlet

1.1DispatcherServlet 类图

1.2 初始准备阶段

1.2.1 init（）

HttpServletBean类中init（）方法

public final void init() throws ServletException {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Initializing servlet '" + this.getServletName() + "'");
}
try {
PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
this.initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
} catch (BeansException var4) {
this.logger.error("Failed to set bean properties on servlet '" + this.getServletName() + "'", var4);
throw var4;
}

this.initServletBean();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Servlet '" + this.getServletName() + "' configured successfully");
}

}

DispatcherServlet的初始化过程主要是通过当前的servlet类型实例转换为BeanWrapper类型实例，

以便使用Spring中提供的注入功能进行对应属性的注入。如ContextAttribute、contextClass、 namespace\

contextConfigLocation等，都可以在web.xml文件中以初始化参数的方式配置在servlet的声明中。

1.2.2 initServletBean（）

 FrameworkServlet的initServletBean（）

this.webApplicationContext = this.initWebApplicationContext();
this.initFrameworkServlet();

this.webApplicationContext = this.initWebApplicationContext();
this.initFrameworkServlet();
protected WebApplicationContext initWebApplicationContext() {
//从ServletContext中获得根容器
WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)wac;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
cwac.setParent(rootContext);
}

this.configureAndRefreshWebApplicationContext(cwac);
}
}
}

if (wac == null) {
wac = this.findWebApplicationContext();
}

if (wac == null) {
wac = this.createWebApplicationContext(rootContext);
}

if (!this.refreshEventReceived) {
this.onRefresh(wac);
}

if (this.publishContext) {
String attrName = this.getServletContextAttributeName();
this.getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + this.getServletName() + "' as ServletContext attribute with name [" + attrName + "]");
}
}

return wac;
}

createWebApplicationContext ()以根容器为父容器创建新的容器，所以在新创建的容器中找不到的bean可以在根容器中找到。

1.2.3 onRefresh()

protected void onRefresh(ApplicationContext context) {
this.initStrategies(context);
}
protected void initStrategies(ApplicationContext context) {
this.initMultipartResolver(context);
this.initLocaleResolver(context);
this.initThemeResolver(context);
this.initHandlerMappings(context);
this.initHandlerMappings(context);
this.initHandlerExceptionResolvers(context);
this.initRequestToViewNameTranslator(context);
this.initViewResolvers(context);
this.initFlashMapManager(context);
}

这里就是DispatherServlet初始化的地方。其中我们重点关注initHandlerMappings()、 initHandlerMappings（);

以initHandlerMappings（）为例，主要是从容器中获得类类型为HandlerMapping.class的bean并存储在list中。如果找不到则获取DispatchServlet.properties文件中默认的两个HandMapping.

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

DispatcherServlet.properties

static {
try {
ClassPathResource resource = new ClassPathResource("DispatcherServlet.properties", DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
} catch (IOException var1) {
throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + var1.getMessage());
}
}

默认资源加载

private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList(matchingBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
} else {
try {
HandlerMapping hm = (HandlerMapping)context.getBean("handlerMapping", HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
} catch (NoSuchBeanDefinitionException var3) {
;
}
}

if (this.handlerMappings == null) {
this.handlerMappings = this.getDefaultStrategies(context, HandlerMapping.class);
if (this.logger.isDebugEnabled()) {
this.logger.debug("No HandlerMappings found in servlet '" + this.getServletName() + "': using default");
}
}

}

1.3功能实现

一句话概括流程：根据request对象获得对应的handler,然后得到对应view，最后对view进行渲染。

DispatcherServlet中doService()、doDispatch().

1.3.1 doDispatch(）

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;

WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

try {
ModelAndView mv = null;
Exception dispatchException = null;

try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);

// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}

// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}

// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

if (asyncManager.isConcurrentHandlingStarted()) {
return;
}

applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}

1.3.1.1 getHandler()

完成URL与Handlerd的映射关系。

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}

简单理解从request中获得url，使用HandlerMapping获得HandlerExecutionChain，注意，这个执行链中包括了HandlerInterceptor和handler。

HandlerInterceptor接口

如同拦截器一般，依次执行上述方法。

1.3.1.2 getHandlerAdapter

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
for (HandlerAdapter ha : this.handlerAdapters) {
if (logger.isTraceEnabled()) {
logger.trace("Testing handler adapter [" + ha + "]");
}
if (ha.supports(handler)) {
return ha;
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}

getHandlerAdapter方法,如同名字一样，获得handler的适配器，handler的实现多种多样，但是我们要定义一个统一的接口来使用handler，

ex:

public class HttpRequestHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof HttpRequestHandler);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((HttpRequestHandler) handler).handleRequest(request, response);
return null;
}
@Override
public long getLastModified(HttpServletRequest request, Object handler) {
if (handler instanceof LastModified) {
return ((LastModified) handler).getLastModified(request);
}
return -1L;
}
}

public class SimpleControllerHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof Controller);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return ((Controller) handler).handleRequest(request, response);
}
@Override
public long getLastModified(HttpServletRequest request, Object handler) {
if (handler instanceof LastModified) {
return ((LastModified) handler).getLastModified(request);
}
return -1L;
}
}

public class SimpleServletHandlerAdapter implements HandlerAdapter {
@Override
public boolean supports(Object handler) {
return (handler instanceof Servlet);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
((Servlet) handler).service(request, response);
return null;
}
@Override
public long getLastModified(HttpServletRequest request, Object handler) {
return -1;
}
}

参考资料：

《SPRING技术内幕：深入解析SPRING架构与设计原理》

《Spring源码深度解析》

《深入分析Java  Web技术内幕》